LibGfx: Re-structure the whole initialization pattern for image decoders

When trying to figure out the correct implementation, we now have a very
strong distinction on plugins that are well suited for sniffing, and
plugins that need a MIME type to be chosen.

Instead of having multiple calls to non-static virtual sniff methods for
each Image decoding plugin, we have 2 static methods for each
implementation:
1. The sniff method, which in contrast to the old method, gets a
    ReadonlyBytes parameter and ensures we can figure out the result
    with zero heap allocations for most implementations.
2. The create method, which just creates a new instance so we don't
    expose the constructor to everyone anymore.

In addition to that, we have a new virtual method called initialize,
which has a per-implementation initialization pattern to actually ensure
each implementation can construct a decoder object, and then have a
correct context being applied to it for the actual decoding.

1 files changed, 8 insertions, 3 deletions

diff --git a/Userland/Libraries/LibPDF/Filter.cpp b/Userland/Libraries/LibPDF/Filter.cpp
index 8898e010eb..976c3be9de 100644
--- a/Userland/Libraries/LibPDF/Filter.cpp
+++ b/Userland/Libraries/LibPDF/Filter.cpp
@@ -269,9 +269,14 @@ ErrorOr<ByteBuffer> Filter::decode_jbig2(ReadonlyBytes)
 
 ErrorOr<ByteBuffer> Filter::decode_dct(ReadonlyBytes bytes)
 {
-    Gfx::JPGImageDecoderPlugin decoder(bytes.data(), bytes.size());
-    auto frame = TRY(decoder.frame(0));
-    return frame.image->serialize_to_byte_buffer();
+    if (Gfx::JPGImageDecoderPlugin::sniff({ bytes.data(), bytes.size() }).release_value_but_fixme_should_propagate_errors()) {
+        auto decoder = Gfx::JPGImageDecoderPlugin::create({ bytes.data(), bytes.size() }).release_value_but_fixme_should_propagate_errors();
+        if (decoder->initialize()) {
+            auto frame = TRY(decoder->frame(0));
+            return frame.image->serialize_to_byte_buffer();
+        }
+    }
+    return AK::Error::from_string_literal("Not a JPG image!");
 };
 
 ErrorOr<ByteBuffer> Filter::decode_jpx(ReadonlyBytes)